1. Field of the Invention
The invention relates to a scan linearization device, and more particularly to a device for introducing external electrical excitation representing images into a nonlinear scanning system which transforms incoming radiant energy into a visible real time image so as to produce undistorted visible images.
2. Description of the Prior Art
A number of systems have been developed which permit night viewing of objects, terrain and the like. Such systems have many applications, including military use for permitting operators of aircraft, artillery, and other weapons systems to obtain visible images of targets in the dark. Such systems generally utilize an optical system which collects radiant energy in the infrared region and converts such energy to a visible image in real time. The present invention is an accessory for use with a night imaging system in which the optical system utilizes scanning which is inherently nonlinear and in which the nonlinearities involved in the radiant energy conversion system are compensated so as to produce a linear visible image. In this night imaging system, it is necessary to produce symbols and other images to be superimposed on the visible image by means of external circuits. The system scanning mechanism which scans the radiant energy to produce visible images unfortunately produces various types of distortion in such externally introduced symbols and images.
For a better understanding of the present invention and the description provided hereinafter, U.S. Pat. No. 3,781,559 issued to Cooper, et al and assigned to Texas Instruments, Incorporated, is hereby incorporated by reference. This patent, entitled "Variable Field of View Scanning System", describes the device to which the present invention is particularly applicable.
The invention described in the referenced patent is a system which transforms incoming infrared radiant energy into a visible real time image. In particular, the device is concerned with producing images having different fields of view, and uses scanning mirrors and an afocal optical section to vary the field of view as required. The afocal section accepts incoming collimated radiant energy to produce exiting collimated energy having a different beam diameter to change the field of view of the system without modifying the basic scanning optics. The collimated radiant energy is caused to scan onto a plurality of detectors in a vertical line. The output of the detectors modulates a vertical array of light emitters to produce a visible image. The image may be viewed directly or a television vidicon may be focused on the scanned image to produce a video signal available for driving a television display which may produce a remote visible image of the incoming radiant energy. As described in more detail in the referenced patent, the scanning system involves a number of moveable lenses and mirrors used in the scanning process and in the desired variable field of view. Nonlinearities in the scanning process may be caused by play in mechanical parts, mechanical jitter, and in the scan control circuitry.